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Questions tagged [luminosity]

Luminosity is the energy radiated from a body per second.

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If a star's luminosity doubles, does its received flux double?

If the luminosity of a star increases or decreases in some way, would the received flux increase or decrease by the same amount (linearly) or would it change by the square of the luminosity (inverse ...
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Is there a way to calculate the habitable zone distances of a star?

What would you need to calculate the habitable zone distances of a star? I am aware of the Stefan-Boltzmann Law and Wein's Law to calculate the Luminosity of the star, and that the flux decreases with ...
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Luminosity and absolute magnitude relationship

Context : an exercise gives the temperature, mass, distance and apparent magnitude of Sirius B and asks to calculate its density. One key step of the calculation is to get the luminosity from the ...
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Luminosity of stars

Good afternoon, I am attempting to calculate the ratio of temperature and luminosity between two stars, one entirely made of iron and the other of hydrogen, with the same volume. To do so, I have ...
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How do we realistically calculate the monochromatic flux of an object in space?

If the collecting area of a telescope is ∆A, and it collects light for a time interval of ∆t, do we just build a telescope with a very small ∆A and make ∆t and ∆λ very small as well? Also, how do we ...
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Given a star's luminosity and a distance from said star, how can I get lux?

Today I wish to know how bright interstellar space is by calculation. I have a dataset of 1000 stars which includes their luminosities. But how do I get illuminance (lux) from luminosity (watts) from ...
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Luminosity distance relation for z around 2? SH0ES Hubble constant

Is there a luminosity distance formula valid for redshift z in range 1-3? Shouldn't this include a term for the current time derivative of the deceleration parameter (q dot)? The only luminosity ...
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Clocks at different redshift: does calculating luminosity distance shift the frame of reference?

Luminosity is energy per time. When we calculate a luminosity distance, using angular diameter distance times $(1+z)^2$, I think we are correcting the energy (from redshifted photons) by $(1+z)$ and ...
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How can there be supermassive stars of 10000+ solar masses?

Wouldn't such supermassive stars blow themselves apart first via radiation pressure (per the Eddington limit)? But they apparently exist, or at least are plausible: Assistant Research Fellow, Ke-Jung ...
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Derivation of the Eddington limit

The Eddington limit can be shown as: Momentum of a photon: $ p = E/c = h\nu / c $ Force due to this radiation is change in momentum. Supposedly then, $$ F_{rad} = \int^\inf_0 \frac{L_\nu}{h\nu}\frac{h\...
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$y$-axis on HR diagram

I have an exercise where I have to determine the luminosity of a star with 10 000K. However, I'm confused about how to read off the $y$-axis on the graph when the scale is uneven. What is the function ...
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Temperature estimate from eclipsing binary

So assuming perfect edge on eclipsing binary, we can estimate the temperature ratio of the two stars because the "blocked area" is the same, and thus the amount of light "dimmed" ...
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Can the equation between apparent brightness and luminosity be applied to lux and lumens?

The equation $b=L/4πd^2$ (where $b$ is apparent brightness in $W/m^2$, $L$ is luminosity, $d$ is distance to a star (or in this case to a torch)). I'm completing an experiment, but I can't find a ...
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Luminosity of an elastic proton-proton scatter

Suppose you have a proton beam ($E=500\,\textrm{MeV})$ with a current of $$6 \cdot 10^{-12}\,\textrm{A} $$ that is colliding with a gaseous hydrogen target which is $3\,\textrm{cm}$ thick. The total ...
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Change in absolute magnitude caused by a change in apparent magnitude

Imagine that we have an object with apparent magnitude $m_1$, later, we observe that the same object appears with an apparent magnitude $m_2 = m_1 + \alpha$, then what we can say about the absolute ...
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How to calculate luminance, given a light source's luminous intensity?

For example, let's suppose I have $2.5$ mm diameter LED with a diffuse lens; it has luminous intensity of $2.0$ cd. Let's say it has viewing angle of 120 degrees and I'm viewing it head on. How would ...
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How to calculate Irradiance in $\rm W/m²$ from experimental data?

i have read some questions previously asked here, but still need help. See, i need to guarantee that a closed space(1x1x0.8m) is receiving 1,12 kW/m² of light. I am using a 250W Siccatherm lamp, that ...
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Calculating photographic exposure - confused about luminance, illuminance, luminosity etc

On first glance this sounds like a photography SE question, but it's more concerned with physical measurement of luminosity, luminance etc - the photographic application of the value calculated is ...
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How to calculate change in absolute magnitude due to a change in stellar radius?

Suppose that the radius of a star increases by some factor, how does this affect the absolute magntiude of the star? I know that $M_1 - M_2 = \Delta M = 2.5 \log \frac{L_1}{L_2}$, so if I knew the ...
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Why does the estimation of the distance of supernovae depends on the cosmological model?

I was reading a paper from arxiv (https://arxiv.org/abs/1312.5798) when I stumbled upon this passage at pag 4 "However, even at low redshifts, there are limitations to how well the Type Ia ...
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What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions?

What part of the photons emitted from a star are from black body radiation and what part originate from fusion reactions? To my understanding these are the two sources of luminosity for a star, so I'm ...
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Is the inverse square law affected by the surface size of the Lightsource?

Lets say I have 2 fully illuminated lighsources. Lightsource A and B. B has 10 times larger illumining surface than A. Both have the same distance from the point of mesurement (in lux). By the "...
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Does luminous efficacy differ between direct and reflected sunlight?

With the total visible light flux being equal does reflected sunlight (by the sky, environment or shading/light redirecting surfaces) have a smaller total energy per luminous flux and therefore ...
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Luminance relation between LEDs when connected in series

I am reviewing a homework problem where we are given three LEDs; in the blue ($450$ nm), in the green ($550$ nm) and in the red ($650$ nm). We are told that the current efficiency $$\eta=\frac{...
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Looking for ideal calibration standards for UV / visible fluorescence

I am attempting to measure the fluorescence timing distribution (how much light is emitted over time from initial excitation) of a substance and I would like to use a solid calibrated sample (some ...
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Convert cps units to candelas / sq. meter

Spectra photometer was reported to measure luminance at given cps rate (counts per second). Is it enough data to know which luminance value it measured, given model and vendor are known?
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What could be the meaning of "illuminance" in this home device?

I bought a Xiaomi sensor that measures light intensity. The data I get from it is called illuminance_lux and the unit is supposed to be ...
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Equations for developing a hypothetical Solar System

I am currently going down the rabbit hole of writing a story but I would like it to be set in a universe which is believable. Therefore I am trying to create a hypothetical solar system in which the ...
LearnedStudent's user avatar
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How do we experimentally estimate the luminosity of a distant star?

While calculating the matter density of the universe, we need to find luminosity. How do we experimentally estimate the luminosity of a star?
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Why the factor $(1+z)^4$?

I am reading through Gravitation by Misner, Thorne and Wheeler. In the exercice 29.5 (page 794) it is asked to calculate the flux of energy $S$ for a distant source in a flat spacetime. The end ...
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Does the $M/L$ ratio have an implied band?

When I look at the NED database, I see the Luminosity quoted for six different bands (X-Ray, UV, Visible, Near IR, Far IR, Radio). My issue is trying to interpret the $M/L$ ratios I've seen ...
Quark Soup's user avatar
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What is the luminosity of the Milky Way?

This question may appear to be the same as What is the luminosity of the Milky Way galaxy?, but that question references a value of $5\times 10^{36}\space W$, which comes from a Wiki page which ...
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Apparent magnitude vs. absolute magnitude

Star Zeta Puppis lies at a distance $460$ pc from Earth. Its apparent visual magnitude $m_V$ is $2.25$, its absolute bolometric magnitude $M_{\mathrm{bol}}$ is $-9.9$, and its angular diameter is $4....
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Does Olber's paradox imply a bright sky or a divergent one

Doing Olber's paradox with specific systems is simple enough. Take stars on a grid of length $\ell$, then the total luminosity is just \begin{equation} L = \sum_{i,j,k} \frac{L_0}{4\pi\ell^2(i^2+j^2+...
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How far should be a supernova to not be seen from Earth?

Hubble sphere is the limit of seeing objects from Earth. But if it wasn't like that would it be possible to see a supernova just because of luminosity over that distance. In simple words would a ...
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Finding exposure time of a satellite camera

Note: I am not sure if this is the correct stack for this question I'm working on a cubesat project, specifically on the camera payload. I've been tasked to find the exposure time of a VIIRS ...
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Solid angles in integral?

Could somebody explain why we have to integrate over the solid angle when calculating total luminosity in the following: The integral over the wavelength makes sense, that a=way we have a total power ...
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Is there a Mass-Temperature relationship for main sequence stars?

When finding relationships between various properties of stars, I frequently find next to nothing on the Mass-Temperature relationship. I, of course, see the Mass-Luminosity and the Luminosity-...
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Why is there no blue peak in the photopic luminosity function?

A luminosity function "describes the average spectral sensitivity of human visual perception of brightness". My understanding is that basically, for the same power, we perceive green light as ...
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How to convert contrast ratio to number of stops?

I have read an article from the below link about the human eye sensitivity and came to know that its dynamic contrast range is 1000000:1 or in other words 30 stops. They also mentioned static contrast ...
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Luminosity of the sun

How is it that the total power generated by nuclear reaction in the core of Sun exceeds its total luminosity? Where does the difference go?
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Magnetic flux density compard to other definition of flux

With regards to flux i have always assumed it was defined as $$(1) Something/m^2s$$ For instance $Luminosity/(4\pi r^2)$ Is an example of radiation flux. Why then is faradys law often cited as the ...
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Luminostiy, Flux, Intensity definitions and meaning

I am taking astrophysics course and we are constantly talking about Luminosity,Brightness,Intensity,Flux etc. I thought that I understand the idea properly but I see now that I dont. Intensity is the ...
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Why is the relation between luminosity distance $d_L$ and comoving distance $\chi$ $d_L=\chi/a$?

The textbook (Scott Dodelson, Modern Cosmology, Section 2.2 Distance, Page 35-36) states the following: Another way of inferring distances in astronomy is to measure the flux from an object of known ...
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Luminosity of a white dwarf

Why in an H-R diagram the white dwarfs are at the bottom left? I understand that they would have a high temperature when they are formed, and so at that instant shouldn't they have a high luminosity ...
Megan mars's user avatar
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2 answers
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Finding the distance to a distant star using standard candles

I understand how we can measure the luminosity of a close star through absolute and apparent magnitude, because we can easily find the distance through trigonometric parallax. What I have understood ...
Megan mars's user avatar
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1 answer
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What is the closest distance for an undiscovered old neutron star and how long would it take to get here? To help people scared of neutron stars

This is to help people who are scared of neutron stars. My questions are What is the faintest a neutron star could be How close could it be and not yet be detected How long would it take to get here ...
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Stephan Boltzmann law

I was preparing for INAO when I came across the application of Stephan Boltzmann law...it's says that energy absorbed per unit time by a planet is Flux times πr^2. But why did we multiply with πr^2 or ...
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Do bigger stars emit higher amplitude waves?

So I’ve been reading about luminosity and I get the concept of the size and temperature determining the intrinsic brightness and total energy emission of the star. I also understand how the further ...
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Where can I find values for apparent brightness of stars?

I'm in high school and doing a project. I want to calculate the distance to stars using their luminosity and apparent brightness, from the equation $b=\frac{L}{4 \pi d^2}$. I have found values for ...
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